Described herein are improved amino-functional release agents for the fusing of electrostatic toner particles. More specifically, herein are described amino-functional release agents, and to fuser members coated or impregnated therewith, that exhibit advantages such as long fuser release life, good adhesion of articles such as 3M Post-It® notes to prints made therewith, and the like. One embodiment is directed to a fuser member comprising a substrate, a layer thereover comprising a polymer, and, on the polymeric layer, a coating of a release agent comprising a mixture of (a) an organosiloxane polymer concentrate containing amino-substituted organosiloxane polymers, wherein there are amino functional groups on at least some of the polymer molecules of the concentrate, said concentrate having a degree of functionality of from about 0.3 to about 0.4 mole percent, said concentrate having a viscosity of from about 800 to about 1,300 centistokes; and (b) a nonfunctional organosiloxane polymer diluent, said diluent having a viscosity of from about 100 to about 2,000 centistokes; said mixture having a degree of functionality of from about 0.05 to about 0.3 mole percent, wherein the mixture has a viscosity of from about 550 to about 1,300 centistokes, and wherein the ratio by weight of concentrate to diluent is from about 1:2 to about 1:30.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles and pigment particles, or toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which can be the photosensitive member itself, or some other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. To fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner to be bonded firmly to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of from about 90° C. to about 200° C. or higher, depending on the softening range of the particular resin used in the toner. It may be undesirable, however, to increase the temperature of the substrate substantially higher than about 250° C. because of the tendency of the substrate to discolor or convert into fire at such elevated temperatures, particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described. These methods include providing the application of heat and pressure substantially concurrently by various means, a roll pair maintained in pressure contact, a belt member in pressure contact with a roll, a belt member in pressure contact with a heater, and the like. Heat can be applied by heating one or both of the rolls, plate members, or belt members. Fusing of the toner particles occurs when the proper combination of heat, pressure, and/or contact for the optimum time period are provided. The balancing of these variables to bring about the fusing of the toner particles is well known in the art, and can be adjusted to suit particular machines or process conditions.
During the operation of one fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between a pair of rolls, plates, belts, or combination thereof. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is desired in the fusing process that minimal or no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles offset onto the fuser member can subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thereby increasing the image background, causing inadequate copy quality, causing inferior marks on the copy, or otherwise interfering with the material being copied there as well as causing toner contamination of other parts of the machine. The referred to “hot offset” occurs when the temperature of the toner is increased to a point where the toner particles liquefy and a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release properties of the fuser member, and accordingly it is desirable to provide a fusing surface having a low surface energy to provide the necessary release.
To ensure and maintain good release properties of the fuser member, it has become customary to apply release agents to the fuser member during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils, such as polydimethyl siloxane, or substituted silicone oils, such as amino-substituted oils, or the like, to prevent toner offset. In addition, fillers can be added to the outer layers of fuser members to increase the bonding of the fuser oil to the surface of the fuser member, thereby imparting improved release properties.
The use of polymeric release agents having functional groups which interact with a fuser member to form a thermally stable, renewable self-cleaning layer having good release properties for electroscopic thermoplastic resin toners, is described in, for example, U.S. Pat. No. 4,029,827, U.S. Pat. No. 4,101,686, and U.S. Pat. No. 4,185,140, the disclosures of each of which are totally incorporated herein by reference. Disclosed in U.S. Pat. No. 4,029,827 is the use of polyorganosiloxanes having mercapto functionality as release agents. U.S. Pat. No. 4,101,686 and U.S. Pat. No. 4,185,140 are directed to polymeric release agents having functional groups such as carboxy, hydroxy, epoxy, amino, isocyanate, thioether, and mercapto groups as release fluids.
It is desired to select the correct combination of fuser surface material, any filler incorporated or contained therein, and fuser oil. Specifically, it is desired that the outer layer of the fuser member react sufficiently with the selected fuser oil to obtain sufficient release. To improve the bonding of fuser oils with the outer surface of the fuser member, fillers have been incorporated into or added to the outer surface layer of the fuser members. The use of fillers can aid in decreasing the amount of fusing oil necessary by promoting sufficient bonding of the fuser oil to the outer surface layer of the fusing member. It is desired, however, that the filler not degrade the physical properties of the outer layer of the fuser member, and it is also desired that the filler not cause too much of an increase in the surface energy of the outer layer.
With regard to known fusing oils, silicone oil has been the preferred release agent for PFA Teflon coatings for fuser members. Release agents comprising silicone oil, however, do not provide sufficient release properties for toner because the silicone oil does not wet fuser coatings of PFA Teflon. Therefore, a large amount (greater than 5 mg/copy) of silicone oil is required to obtain minimum release performance. Alternatively, a large amount of wax must be incorporated into the toner in order to provide adequate release of the toner from the fuser member.
For other fluoropolymer, and especially fluoroelastomer, fuser member outer layers, amino silicone oil has been the release agent of choice. Amino oil, however, does not diffuse into paper products, but instead reacts with the cellulose in the paper and therefore remains on the surface of the paper. It is believed that hydrogen bonding occurs between the amine groups in the amino oil and the cellulose hydroxy groups of the paper. Alternatively, the amine groups can hydrolyze the cellulose rings in the paper. The amino oil on the surface of the copied paper prevents the binding of glues and adhesives, including attachable notes such as adhesive 3M Post-it® notes, to the surface of the copied paper. In addition, the amino silicone oil present on the surface of a copied paper prevents ink adhesion to the surface of the paper. This problem results in the poor fix of inks such as bank check endorser inks and other similar inks. Similar problems can also occur with mercapto-functional and functional fusing oils, although such problems are usually observed to a lesser extent than with amino-functional fusing oils.
U.S. Pat. No. 6,183,929 discloses amino- and mercapto-functional release agents, and fuser members coated or impregnated therewith, that exhibit advantages such as long fuser release life, good adhesion of articles such as 3M Post-It® notes to prints made therewith, and the like. The Abstract discloses a fuser member comprising a substrate, a layer thereover comprising a polymer, and, on the polymeric layer, a coating of a release agent comprising a mixture of (a) an organosiloxane polymer concentrate containing amino-substituted or mercapto-substituted organosiloxane polymers, wherein there are amino or mercapto functional groups on at least some of the polymer molecules of the concentrate, said percent, said concentrate having a viscosity of from about 50 to about 500 centistokes; and (b) a nonfunctional organosiloxane polymer diluent, said diluent having a viscosity of from about 100 to about 2,000 centistokes; said mixture having a degree of functionality of from about 0.05 to about 0.4 mole percent, wherein the mixture has a viscosity of from about 1,000 to about 2,000 centistokes, and wherein the ratio by weight of concentrate to diluent is from about 1:2 to about 1:30.
While the above release agent solved the problems of release life under minimal stresses, a need still remains for a fuser release agent that will provide extended fuser release life under stressful image conditions, such as higher speeds, higher toner coverage, higher fusing temperatures, and higher stress image sets. An additional need exists for a release agent, which allows the adhesion of post-it, notes, enhanced ability to write on print and bookbinding.